The media is full of information about the effects of too much sun exposure. Unfortunately, most people still link sun exposure to sunburn and only use protection when planning a full day of outside activities. As with most health issues, it is the years of daily short exposures that add up to the most sun damage. Just 10 minutes a day adds up to over an hour of unprotected sun exposure in just one week.
How much time do you spend in your automobile. What about commuting or just running errands? If you thought ultraviolet (UV) light rays couldn't find you in your car think again. While the windshield in most cars is very effective at screening UV, the rest of the windows only absorb a portion of the ultraviolet spectrum. Scientists used to think that the portion of the ultraviolet light that is transmitted through glass was "safe" ultraviolet but research continues to uncover the damaging effects of this higher wavelength UV. Still not a believer? Would you leave your drycleaning hanging in the car for a month? Most people wouldn't dream of leaving valuable clothing in a vehicle because of damage. Yet we drive for years without considering what may be occurring under our skin where the damage won't be seen until it is too late to repair. The most common means of transportation is the automobile but millions of miles and hours are spent in other modes, such as planes, trains, buses, all with various degrees of exposure to the sun.
Without radiation from the sun, the Earth would cease to exist. Sunshine is essential to plant and animal life but there are certain portions of this radiation that the human body could use in much smaller doses. Solar radiation is a form of electromagnetic radiation. Electromagnetic energy exists as waves. The length of one cycle of those waves is called a wavelength. These wavelengths are measured in nanometers (nm) which is 1 billionth of a meter. Different types of energy are distinguished by their "wavelength".
Scientists have split the solar energy from the sun into three bands of wavelengths. These three bands are Ultraviolet (100-400 nm), Visible Light (400-780 nm) and Near Infrared (780-2400 nm). As its name implies, visible light is the light that the human eye can see. Since individuals vary in their ability to detect visible light, the borders surrounding the visible light region are somewhat artificial. Near infrared radiation is the part of the sun's rays that warm the Earth. Ultraviolet is energy from the sun that we can neither see nor feel but these short wavelengths can have a tremendous effect on the human body.
Although ultra-violet light accounts for only 3% of the total solar spectrum, it is the most active part of the spectrum for photodamage. Photobiologists, scientist who study the effects of light on living things, have divided ultraviolet radiation into three groups of wavelengths. UV C (less than 290 nm), UV B (290-320 nm), and UV A (320-400 nm). All UVC and a portion of the UVB radiation is screened by the earth's ozone layer. UVB is screened completely by glass and many types of plastic glazing. UVB is most commonly known as the part of the UV spectrum which causes sunburn and is more potent than the longer wavelength UV A. UV A is not screened by glass and until recently sunscreens did not screen in the UV A region. Most sunscreens still provide very little UV A protection. While UV B is more potent, UV A makes up over 90% of the ultra-violet radiation that reaches the earth's surface. The total amount of UV that reaches the earth's surface varies by season, time of day, and geography. It is highest during summer, midday, and at the equator. It is important to understand that all ultraviolet light is not the same and that different wavelengths of UV may have varied effects on the body.
Most of the important functions of the human body happen inside our outer protective layer. In animals this protective skin layer is further covered by fur or hair but man has very little natural protection for the skin. Few people realize that the skin is the largest organ of the body. The skin is made up of an outer layer called the epidermis and an inner layer called the dermis. The epidermis is in a constant state of renewal. The top layer is in fact composed of flat dead skin cells and is known as the stratum corneum. These cells are shed in microscopic flakes in approximately four week cycles. New living cells from the bottom of the epidermis are constantly being formed and move toward the surface to repeat the cycle. The epidermis protects the body from bacteria and moisture loss.
The dermis layer lies below the epidermis and is up to forty times thicker. The dermis is composed of collagen and elastin fibers that provide support for the blood vessels, nerves, sweat glands, hair follicles, and sebaceous glands that are all a part of healthy functioning skin. Collagen and elastin fibers are important because they help the skin maintain its elastic properties. Damage to this layer leads to sagging and wrinkling of the skin. Fibrocytes, the cells that produce collagen fibers are also found in the dermis. At the interface between the dermis and epidermis are found the melanocytes. These cells contain the pigment melanin which gives skin its color.
The only other human organ which is exposed directly to the sun is the eye. While we have eyelids and eyelashes which offer some protection from dust and light, the eye is generally exposed to all forms of light, especially in young children. The viewing area of the eye is composed of the outer protective mucus membrane, the cornea, the aqueous humor, the iris, the pupil, the lens, the vitreous humor, and the retina. Damage can occur to the lens and the retina by exposure to sunlight. Young children are especially susceptible to retina damage since the lens does not develop its full potential to screen ultraviolet and blue light until adulthood.
The media is flooded with information about the need to wear sunscreen but few people understand the science behind those warnings or the consequences of ignoring them. Ultraviolet radiation has been shown to contribute to all three major types of skin cancer; photoaging of the skin (including wrinkling, pigment changes, and sagging); photosensitivity causing rashes and inflammation; and eye damage including partial blindness and cataracts. There is new research which indicates that ultraviolet radiation may in fact take away some of the body's natural immunity in subtle and specific ways.
The most recent statistics predict the future skin cancer rate will be a million or more cases per year in the United States alone. At that rate, one in six Americans will develop skin cancer during their lifetime according to the report. There are many theories for this increase but whatever the reason the number of cases is rising. While scientists do not know the exact reason for the increase, they are certain that skin cancer is linked to sun exposure.
Cancer is a group of diseases with one thing in common: cells become abnormal, dividing too often and without control or order. These malignant cells form a tumor that can invade and destroy nearby tissue. The cancer cells also can spread throughout the lymphatic system or the bloodstream to other parts of the body and form new tumors. The spread of cancer is called metastasis.
There are three types of skin cancer. The two most common types are basal cell carcinoma and squamous cell carcinoma. These two types account for over 90% of the skin cancer diagnosed in the United States. These are slow growing cancers which seldom spread to other parts of the body. Skin cancers of this type are the most curable. It is currently believed that these types of skin cancer are linked mainly to UV B exposure although UV A is now being studied as well.
The most deadly form of skin cancer is melanoma. Unlike the other two forms of skin cancer, malignant melanoma can quickly spread to other parts of the body if not treated early. There were 35,000 cases of malignant melanoma in 1995 and the number of cases is increasing at 4% per year. Up until recently, it was believed that melanoma was also caused predominantly by UV B. Research at the M. D. Anderson Cancer Center in Houston, Tex. has indicated that while using sunscreen did prevent non-melanoma skin cancers, the sunscreen (which screened mostly in the UV B wave length) had no effect in preventing melanoma. Further evidence of UV A effects came from a study of tanning bed users conducted in Sweden by researchers at University Hospital in Lund. The results were published in the American Journal of Epidemiology, October 1994. Tanning beds use UV A radiation to give users a supposedly "safe" tan. The study found that tanning bed users under the age of 30 who used tanning beds more than 10 times a year had more than seven times the risk of melanoma. At the current rate of melanoma increase that would raise the risk for tanning bed users to about 1 in 13. This research along with other studies makes the case against UV A rays so great that the American Medical Association again recommended (in December 1994) that tanning beds be banned for anything but medical use. While no one is sure how UV A radiation effects the skin, some researchers believe that it lowers the immune system's ability to function properly.
Most people believe that as we get older our skin naturally begins to wrinkle and sag. While that is true to some extent, scientists believe that as much as 80% of these signs of aging it can also lead to permanent loss of vision. The damage is caused by visible blue light and UVA. The prevention for this is the age old adage--never look directly at the sun! Other forms of retina damage can also occur from common exposure to sunlight. Infants, children, and teens are more susceptible to damage from ultra-violet radiation. While the cornea absorbs any radiation below 295 nm, the lens slowly develops its ability to absorb UVA and blue light reaching its full absorption ability at adulthood.
Unfortunately, since the lens develops into a good UV A absorber, it is susceptible to damage caused by too much UV absorption. Since the lens cannot shed damaged cells there is no way for it to repair itself. This damage often leads to cloudy vision and a condition known as cataracts.
Skin cancer, sunburn, pigment spots, rashes, cataracts, retina damage, and wrinkles have all been linked to exposure to ultraviolet radiation. While scientists work on ways to repair this damage, the best possible defense is prevention. It is never too late to start protecting your skin and eyes from UV damage. Ultraviolet screening techniques and limiting sun exposure can prevent further damage and in some cases the damage may be reversible with proper protection. Living in the dark would be as unhealthy to mental well-being as basking in the sun is to the skin and eyes. Using common sense and taking advantage of the ultra-violet screening techniques available will help protect you and your family from the damage caused by the sun's UV rays.